1. Field of the Invention
This invention relates to keyless entry for executing immobilizer authentication. More particularly, the invention relates to keyless entry for executing immobilizer authentication that sequentially executes an authentication process from a transponder having a high possibility of authentication by utilizing a combination of an ID of a mobile device that has already been registered with an ID of a transponder when authentication of the transponder fitted to and used in the mobile device is executed, and shortens an authentication time.
2. Description of the Related Art
As a heretofore known passive remote keyless entry (RKE), a system construction is known in which a mechanical key for starting and operating an ignition of a motorcar can be fitted to a mobile device and a transponder is incorporated, and which has an immobilizer function for giving permission of an engine start through wireless communication. According to this passive keyless entry function, communication is first made between a mobile device and a car-mounted device, the car-mounted device releases door lock of a door on the driver's seat side when the mobile device is authenticated as being proper through that communication, and a driver can then open the door on the driver's seat side and can get into the motorcar. When the car-mounted device communicates with the transponder and authenticates the transponder as being proper through that communication, the immobilizer function permits the starting operation of the ignition. When this setting is made, the driver can start and operate the ignition by use of a mechanical key.
The communication ma-de in this case between the car-mounted device and the transponder is as follows. First, the car-mounted device transmits a request signal containing a password and a cipher code of a random number to the transponder. Next, the transponder returns an answer signal containing an answer message and an ID inherent to the transponder in response to the request signal. Receiving this answer signal, the car-mounted device permits the starting operation of the ignition when it authenticates the answer message and the ID as being correct. This authentication procedure is referred to as “immobilizer authentication”.
Generally, a plurality of mobile devices is used for one car-mounted device in most cases in passive remote keyless entry. In this case, the same number of transponders as that of mobile devices exists. When the numbers of these transponder and mobile device are plural, the number of times of communication made between the transponders and the car-mounted device becomes the same in the worst case as the number of the mobile devices. In consequence, the time until immobilizer authentication is made and the ignition can be started gets elongated, and the driver may feel the waiting time too long.
To shorten such a waiting time as much as possible, means has been employed that stores a transponder to which access is lastly made, and starts an access from the transponder so stored when the next access is made.
The means described above is effective when only one driver uses a motorcar substantially exclusively. When all the members of a family or a plurality of people uses one motorcar as in the case of America and Europe, however, the transponder lastly accessed is not always used next time even when this transponder is stored, and the means cannot be said to be always effective.